In general, before machining is performed on a workpiece using a machining apparatus that is exemplified by an electrical discharge machining apparatus and a laser machining apparatus with high accuracy, a setup process is performed in which a reference surface of the workpiece is aligned relative to the scan axis of the machining apparatus with high accuracy. In the setup process, the workpiece is fixed to a scan unit of the machining apparatus with a fixture, a dial gauge is pressed against the reference surface of the workpiece, and the position of the workpiece is adjusted manually such that the value of the dial gauge does not change when the scan axis corresponding to the reference surface of the workpiece is moved. Such a manual setup process poses a problem in that it takes time and causes variation in the result of the alignment in a manner depending on the skill of operators.
In order to reduce the work time and the variation due to operators, there is a method in which a measurement sensor is attached to the machining apparatus and the setup is performed automatically. Such a measurement sensor includes, in addition to contact type sensors, an optical sensor capable of measuring in a noncontact manner. An optical sensor emits a laser beam toward a top surface of the workpiece and detects the reflected light so as to measure the position of the detected surface in a noncontact manner. Hence, such an optical sensor offers an advantage of enabling measurement of a narrow reference hole and a soft workpiece.
Patent Literature 1 to Patent Literature 3 listed below are known as related techniques.